具有内部泛型的C#转换对象

我正在尝试将具有泛型的具体类转换为其接口并出现错误.我不确定我缺少什么.我需要使它们成为普通类型.

Unable to cast object of type ‘HierarchalLocationFilterSet’ to type ‘ImAFilterSet`1[ModelBase]’.

一切都可以编译并运行,我似乎无法执行以下操作.

ImAFilterSet<IModelBase> c = new HierarchalLocationFilterSet()

我可以走一半

var thisWorks = c as FilterSetBase<LocationModel>;
var thisAlsoWorks = c as ImAFilterSet<LocationModel>;
//This is a hard fail   
var x = ((ImAFilterSet<ModelBase>) c );
var y = ((ImAFilterSet<IModelBase>) c );

给定

public interface ImAFilterSet<C> where C : IModelBase
{
     List<C> Children { get; set; }
}

public abstract class FilterSetBase<C> : ImAFilterSet<C> where C : IModelBase

public class HierarchalLocationFilterSet : FilterSetBase<LocationModel>

public class LocationModel : ModelBase

public abstract class ModelBase : IModelBase

谢谢！

解决方法:

通用类/接口在.NET中默认是不变的.这就是您的代码失败的原因.

投射FilterSetBase< T1>到ImAFilterSet< T2>. T1必须与T2相同.让T1继承T2是不够的.

您可以通过更改FilterSetBase< C>的声明来解决此问题：

public abstract class FilterSetBase<C> : ImAFilterSet<IModelBase>
    where C : IModelBase { }

或者您可以使ImAFilterSet成为协变量：

public interface ImAFilterSet<out C>
    where C : IModelBase { }

仅当您的接口未声明参数类型为C的任何方法/属性时,这才可能.

标签：casting,generics,c
来源： https://codeday.me/bug/20191120/2045250.html